The process of cell injuries owing to ischemia is broadly divided into two courses: (1) damages caused by reduction in intracellular ATP level or increase in intracellular calcium concentration etc. under insufficient oxygen supply during ischemia and (2) damages caused by increasing influx of calcium or production of free radicals, etc. followed by reperfusion or restoration of blood vessels after ischemia (Yoshiwara, et al., Metabolism and disease, 29, 379 (1992)). As typical ischemic diseases, cardiovascular diseases such as variant angina, unstable angina, myocardial infarction and arrythmia brought by reperfusion of coronary arteries by PTCA/PTCR/CABG, etc. or cerebrovascular diseases such as transient cerebroischemic attack, traumatic injury to the head and sequels after brain surgery can be given. In the treatment for variant angina or unstable angina, nitro compounds exemplified by nitroglycerin and nicorandil and calcium antagonists exemplified by diltiazem, nifedipine and verapamil are used and for the myocardial infarction or coronary reperfusion injury followed by PTCA/PTCR/CABG, etc., use of 5-lipoxygenase inhibitors or radical scavengers is under investigation. As a preventive or treating agent for ischemic cerebrovascular diseases, glyceol (registered trade mark), ozagrel, nizofenone, ticlopidine, nicaraven, etc. have been investigated and used with the idea of reducing the occurrence of cerebral edema or cerebrovascular spasms in the acute stage of cerebrovascular accident. In the chronic stage, cerebral circulation enhancers such as calcium antagonists exemplified by nicardipine, cinnarizine and flunarizine, cerebral circulation enhancers with promotive action for metabolism such as vinpocetine, nicergoline, pentoxifylline, and ifenprodil, or cerebral metabolic activators such as idebenone, GABA, and calcium hopantenate have been used in order to increase blood flow or improve the metabolic state in the tissue which survived the ischemic injury.
Based on extensive investigation to seek for an excellent preventive or therapeutic agent for ischemic diseases and an antihypertensive agent which would be able to suppress the generation of active oxygen species and increase of intracellular calcium concentration that are considered as the main causes of ischemic diseases and hypertension, the present inventors have synthesized the compounds represented by formula (I) and found that these compounds concurrently exhibit vasorelaxing activity (calcium antagonism), lipid peroxidation inhibitory action and calcium overload inhibitory action and that they are effective as a preventive or therapeutic agent for ischemic diseases and an antihypertensive agent. The present invention has been accomplished based on the findings.
Disclosure of the Invention
The present invention provides a therapeutic agent for ischemic diseases characterized by containing a compound represented by the general formula (I): ##STR2## wherein R.sub.1 represents a hydrogen atom, a hydroxyl group, an acyloxy group having 1 to 9 carbon atoms or a lower alkoxy group having 1 to 6 carbon atoms; R.sub.2 and R.sub.3, which may be the same or different, each represents a hydrogen atom, a hydroxyl group, a halogen atom, a lower alkyl group having 1 to 6 carbon atoms or a lower alkoxy group having 1 to 6 carbon atoms; R.sub.4 represents a hydrogen atom, a lower alkyl group having 1 to 6 carbon atoms; A represents a fragment represented by formula (II): ##STR3## wherein R.sub.5 represents a hydrogen atom, a substituted or unsubstituted lower alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted lower alkenyl group having 1 to 6 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group, or R.sub.5 forms a 5- or 6-membered ring containing two or more oxygen atoms or sulfur atoms, in which case the carbon atom to which it is bonded is a spiro atom; or a fragment represented by formula (III): EQU B (III)
wherein B represents a fragment selected from the group of following fragments represented by formulae (IV), (V), (VI), (VII), (VIII), (IX), (X), (XI), (XII), (XIII), (XIV), (XV), and (XVI): ##STR4## R.sub.6 and R.sub.7, which may be the same or different, each represents a hydrogen atom, a substituted or unsubstituted lower alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted lower alkenyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group or a substituted or unsubstituted heterocyclic group, provided that R.sub.6 and R.sub.7 do not represent a methyl group simultaneously, or R.sub.6 and R.sub.7 are taken together to form a substituted or unsubstituted ring which may be a condensed ring; and n represents an integer of 2, 3, 4, 5 or 6; or a pharmaceutically acceptable salt thereof or a possible stereoisomer or optical isomer thereof as an active ingredient.
In the compounds represented by the general formula (I), examples of the substituents which may be present on the lower alkyl group having 1 to 6 carbon atoms, lower alkenyl group having 1 to 6 carbon atoms, lower alkoxy group having 1 to 6 carbon atoms, aryl group or heterocyclic group include halogen atoms such as chlorine and bromine atoms; a hydroxyl group; a carboxyl group; alkoxycarbonyl groups such as methoxycarbonyl and ethoxycarbonyl groups; carbamoyl groups such as N,N-dimethylcarbamoyl group; alkoxy groups such as methoxy and ethoxy groups; phenoxy groups such as 3,4-methylenedioxyphenoxy, 3,4,5-trimethoxyphenoxy, 3,4-dimethoxyphenoxy and 4-methoxyphenoxy groups; and phenyl groups such as 3,4-methylenedioxyphenyl and 4-methoxyphenyl groups.